A Schottky barrier diode (i.e., SBD) includes a Schottky electrode, which contacts a semiconductor layer. An interface between the Schottky electrode and the semiconductor layer has a small work function between metallic material composing the Schottky electrode and semiconductor material composing the semiconductor layer. Accordingly, when a reverse voltage is applied to the diode, a leak current in the SBD is larger than a PN junction type diode.
JP-2000-294804 discloses a construction having a Schottky junction and a PN diode. Specifically, the PN diode is formed in a part of the Schottky junction, so that a leak current is reduced when a reverse voltage is applied to the construction. More specifically, a Schottky electrode contacts a N− type drift layer at a contact region, which provides a terminal structure (i.e., an outer periphery breakdown region). The terminal structure has a RESURF layer. A surface portion of the drift layer and a P type layer having a concentric pattern are arranged on an inner side of the RESURF layer. Thus, the PN junction diode is formed in a part of the Schottky junction.
This is a junction barrier Schottky (i.e., JBS) structure having two types of electronic property, which are Schottky diode property and PN diode property. The Schottky diode property provides I-V (i.e., current-voltage) characteristics such that the diode breaks down at a comparatively small voltage, and then, the current increases with a predetermined slope with respect to voltage increase. The PN diode property provides I-V characteristics such that the diode breaks down at a comparatively large voltage, and then, the current rapidly increases in avalanche manner.
In a conventional JBS structure, it is necessary to contact the Schottky electrode on the N− type drift layer with Schottky contact. Thus, the Schottky electrode is made of metallic material capable of forming a Schottky barrier. Therefore, it is difficult to provide ohmic contact with the P type layer, thereby, it is difficult to utilize the advantage of the JBS structure effectively.
Thus, it is required to contact the Schottky electrode and an impurity layer composing the PN diode with the ohmic contact.